Collaborative Research: Comprehensive Analysis of Seismic Processes in a Deep South African Mine

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Many fundamental questions in earthquake physics remain unresolved, largely because ofdifficulties in obtaining high-quality, near-source recordings of small earthquakes andderiving reliable source parameters. The overarching goal of this project is to provide animproved understanding of earthquake source processes for a wide magnitude range(approximately -4 to 4). We are performing detailed seismological investigations ofsource properties that characterize several distinct classes of seismic events (earthquakes,rockbursts, and blasts) in a 3.6 km deep South African mine. We will also conduct a shortfield campaign to record seismic events at the extremes of the magnitude range and inclose proximity to fault structures. Full source tensor inversions, second momentanalysis, and spectral methods will be used to determine comprehensive sets of sourceproperties including scalar potencies/moments, focal mechanisms, corner frequencies,strain/stress drops, radiated energies, rupture velocities, and source time functions.Special effort will be devoted to detecting isotropic components of faulting. Theoreticalcalculations of expected radiation from different event types will help in theinterpretation of results.Applying the above analysis to the small-magnitude, near source seismic data will allowus to obtain constraints on many aspects of earthquake physics including nucleationprocesses, the prevalence of isotropic components of seismic radiation, changes in thephysics of rupture with event magnitude or with proximity to geologic and miningstructures, and source parameter differences between earthquakes, explosions, and otherseismic sources. The high-resolution results on seismic source properties and scalingrelations will significantly impact the earthquake physics and rock mechanicscommunities by helping to resolve long-term controversies on earthquake nucleation andrupture processes, scaling of laboratory results to natural faults, and earthquake energybudgets, among others. In addition, the findings on spatially dependent seismic propertieswill be useful for decision-making concerning when and where to suspend miningactivities to enhance underground safety